[Python-ideas] Name mangling removal ?

Guido van Rossum guido at python.org
Sun Feb 1 23:34:23 CET 2009

On Sun, Feb 1, 2009 at 2:29 PM, Steven D'Aprano <steve at pearwood.info> wrote:
>> E.g. consider person A who writes a library containing a class
>> A, and person B who writes an application with a class B that
>> subclasses A. Let's say B needs to add new instance variables, and
>> wants to be "future-proof" against newer versions of A that might add
>> instance variables too. Using name-mangled variables gives B a
>> "namespace" of his own (_B__*), so he doesn't have to worry about
>> clashes between attribute names he chooses now and attribute names
>> that A might choose in the future. Without name-mangling, B would have
>> to worry that A could add private variables with clashing names as
>> well -- in fact, the presence of any private variables in A would have
>> to be documented in order to ensure that subclasses wouldn't
>> accidentally clash with them, defeating the whole purpose of private.

> Just for completeness sake, I'll point out that there is still a possible
> name clash using name-mangling: if you subclass B, and inadvertently name
> your subclass A (or any other superclass of B), then your __names may clash
> with A's __names.

Of course. But that's several orders of magnitude easier to avoid,
since classes are so much rarer than attributes.

> I don't particularly like name-mangling, but I don't see it is a large
> enough problem that it needs to be removed, particularly in the absence of
> any viable alternative.

I usually recommend against it (in favor of a single underscore), but
there are a few situations where it is really useful.

--Guido van Rossum (home page: http://www.python.org/~guido/)

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